Rational shape control of porous Co₃O₄ assemblies derived from MOF and their structural effects on n-butanol sensing

Porous metal oxides are promising materials for VOCs (volatile organic compounds) chemical sensors, because they have large specific surface areas and enough internal space for the fast gas diffusion. Recently, metal-organic framework (MOF) materials with varied shapes and sizes have been regarded as good templates for preparing porous metal oxides. Herein, four kinds of Co-MOFs were prepared by altering the ratios of Co²⁺ ions and 2-methylimidazole at room temperature, which exhibited well-controlled shapes. Then, corresponding porous Co₃O₄ assembled from nanoparticles was acquired by heating Co-MOFs, and showed a good sensing performance for n-butanol, with a response up to 21.0 toward 100 ppm n-butanol. Moreover, it is found that the shape and the size of Co₃O₄ assemblies can significantly influence their sensing performances. For porous Co₃O₄ assemblies, when the nanoparticles are small enough (˜10 nm), a porous structure with a larger proportion of the nanoparticles close to its surface tends to show a better gas-sensing performance. The findings can be used in the design of gas-sensing materials in the future.